(1) Field of the Invention
This invention relates to a communication device provided with a plurality of electronic circuit boards, such as a platform information communication device, a cooling fan unit and an operation control method for the cooling fan unit, and more particularly, to a communication device comprising multiple electronic circuit boards mounted to a back wiring board (BWB).
(2) Description of the Related Art
A conventional cooling structure for an electronic unit is disclosed in Japanese Unexamined Patent Application No. 05-259673, for example. According to this publication, a cooling system is constructed by mounting a cooling fan to an electronic unit constituted by a combination of intense heat-generating communication devices, such as electronic exchanges, such that air is forced to flow through the interior of the electronic unit. In this cooling system, the intense heat-generating communication devices are provided with fins, in order to reduce the size of the heat radiator of the electronic unit and thereby reduce the size and weight of the unit, and cooling air is forced to flow along the fins by an axial fan.
FIG. 19 is a side view schematically showing the construction of a communication device using a conventional cooling system.
The cooling system for the communication device 1 has axial fans arranged on cooling air inlet and outlet sides, respectively, and is generally called push-pull type. A fan unit 100 constituted by two axial fans 101 and 102 serves to suck cooling air coming from an air inlet 110 arranged at a lower portion of the device into the interior of the communication device 1. A discharge fan unit 200 is adapted to dispel heat to outside from an air outlet 210 arranged at an upper portion of the communication device 1, and is constituted by two axial fans 201 and 202.
A plurality of electronic circuit boards (not shown), for which the cooling system is provided, are inserted as a plug-in unit (PIU) into the communication device 1 from the front side thereof such that the boards are directed vertically between the two fan units 100 and 200 and arranged side by side. Arrow A appearing in the left part of FIG. 19 indicates the direction of insertion of the electronic circuit boards.
In the conventional cooling system, the four axial fans 101, 102, 201 and 202 are operated at all times to function as a push-pull type fan system so that heat can be dispelled to outside from the communication device 1. Thus, the communication device 1 needs to include spaces for containing the two fan units 100 and 200, respectively, a space for containing a shielding plate 111 which allows air to be introduced into the intake fan unit 100 from the air inlet 110 at the lower portion of the front of the communication device, and a space for containing another shielding plate 211 which guides the air from the discharge fan unit 200 toward the air outlet 210 at the upper portion of the back of the communication device.
In the push-pull type cooling system constituted by axial fans as described above, the cooling air is sucked in and discharged both in a horizontal direction, as indicated by arrows B and C, respectively, in FIG. 19. Accordingly, the communication device 1 inevitably has an increased size which is larger than the width or height of the electronic circuit boards by an extra amount corresponding to the thicknesses of the axial fans of the fan units 100 and 200 and the spaces allotted to the air inlet 110 and outlet 210. Also, in the case of the conventional communication device 1 in which the electronic circuit boards as a plug-in unit are positioned horizontally and arranged one above another, the cooling air cannot be smoothly sucked in and discharged when a plurality of such communication devices are mounted on a rack.